Site-Selective γ-Trihalomethylation and γ-Dihalomethylidenation of Silyl Dienol Ethers under Organophotoredox Catalysis

We report a general remote tribromo- and trichloromethylation process using CBr4 and CBrCl3 as ready available sources of trihalomethyl radicals. This method operates under mild and metal-free photocatalyzed conditions and enables the access to gamma-trihalomethylated enals with complete regioselectivity in up to 71 % isolated yield. Importantly, this protocol is easily adapted to the selective one-pot synthesis of the corresponding gamma-dihalomethylidenated enals in up to 49 % overall yield. Mechanistic studies are in favor of a radical chain propagation initiated by an oxidative quenching of the photocatalyst.